This creates a set of substitution rules to replace all current usages
of SDK versions in the documentation, apart from a few that were not
meant to be copy-pastable anyway and the version has just been swapped
with a <version> placeholder.
Since code-block does not parse the content, these have all been
replaced with parsed-literal. That one though parses URLs, which cannot
be broken, so a series of URL substitutions are provided too.
Signed-off-by: Fabio Baltieri <fabiobaltieri@google.com>